{
    let fn=(...arg)=>{
        console.log(arg);
        console.log(arg.length);
        console.log(arg[0]);
    }
    fn(1,2,3,4,5);
}
{
    let span=document.getElementsByTagName("span");
    //span.push('a'); 不是数组
    let arr=Array.from(span);
    arr.push('a'); 
    console.log(arr);
}
{
    console.log(Array.of(1,2,3,4,'a'));
}
{
    console.log([1,2,3,4,5].copyWithin(0,3,4));
}
{
    let arr=['a','b','c','d'];
    console.log(arr.find((item)=>{
        return item=='c';
    }));
    console.log(arr.findIndex((item)=>{
        return item=='c';
    }));
}
{
    let arr=['a','b','c','d'];
    // console.log(arr.fill('o'));  //['o', 'o', 'o', 'o']
    console.log(arr.fill('o',0,3)); 
}
{
    let arr=['a','b','c'];
    //数组的key 0 1 2  数组的value   a b c
    for(let k of arr.keys()){
        console.log(k);
    }
    for(let v of arr.values()){
        console.log(v);
    }
    for(let [k,v] of arr.entries()){
        console.log(k,v);
    }
}
{
    let arr=['a','b','c'];
    console.log(arr.indexOf('a'));
    console.log(arr.includes('a'));
    console.log(arr.indexOf('o'));
    console.log(arr.includes('o'));
}